1. Field of the Invention
The present invention relates to image synthesis for producing a new image by performing calculations for a plurality of images.
2. Description of the Prior Art
As a method for obtaining images irradiated with light from any position for an actual 3-dimensional object, as shown on pages, 97 to 104 in ┌Graphics and Visionxe2x80x94Digital Image Processing┘ by Masayuki Nakajima and Masanobu Yamamoto, Ohmsha, Ltd., 1996, a method shown in the following is generally known. In the method, the 3-dimensional coordinates of a plurality of characteristic points on the surface of an object body are measured, and a 3-dimensional geometrical model is constructed by sticking the texture image on the surfaces of the polyhedron which makes these characteristic points apexes, and after that a light source position is provided to perform rendering by ray tracing or the like.
In a conventional method mentioned in the preceding paragraph, there is a difficulty to require many hands or special tools for the measurement of 3-dimensional coordinates on the surface of the object. It requires a lot of calculation quantity for the rendering taking the light source position for the 3-dimensional object into consideration and a long processing time for synthesizing an image, so that there are also difficulties in a case where real time processing is to be performed.
An object of the present invention is to provide a method of synthesizing an image for any light source position and the apparatus therefor from the data which are easily available like images of an object body photographed with a camera without requiring many hands or special tools as generally required in a case where a 3-dimensional geometrical model is constructed.
In order to solve the above-mentioned subject, the present invention adopts a method and a means as described in the following.
The present invention provides a method of synthesizing an image for any light source position and the apparatus therefor in which information concerning at least one of a direction and a color on the surface of an object body to be photographed, is extracted from a plurality of original images photographed at changed light source positions in relation to respective positions of the light source, and an image for any light source position can be synthesized based on the extracted information.
For example, as a simple synthesizing method, it can be considered to take a weighted average of every pixel in the image data when light sources are disposed on the left and the right sides of an object body; however, the image is not synthesized based on a model, so that the relation between the synthesized image and the position of a light source is not clear. Therefore, it is not possible to say that the synthesized image correctly reflects the change of the light source position. As shown on pages, 40 to 43, in xe2x80x9cGraphics and Visionxe2x80x94Digital Image Processingxe2x80x9d by Masayuki Nakajima and Masanobu Yamamoto, Ohmsha, Ltd., 1996, in general, an original color, a normal, the directions toward a light source as well as a view point, all have definite relations between a color actually observed. Therefore, in the present invention, an image is synthesized for any light source position using such relations.
According to the Japanese Patent Laid-open No. Hei 1-143127, an electron microscope is equipped with a plurality of electron detectors. An object body is irradiated from a certain direction with electron beams and the reflected electrons on the surface of the object body are diffused toward respective directions. By measuring the diffusion of electrons, the normals on the surface of the object body are found. In the present invention, similarly to the above, the images of an object body are photographed with light sources disposed in a plurality of different positions, and from the change in colors for the light source positions, that is, from the change in diffusion of light reflected on the surface of the object body, the parameters to be the coefficient for deducing a color which is actually observed from light source positions such as an original color or inclination on the surface of the object body are measured. Using these parameters, an image can be synthesized for any light source position, whereby it is made possible to provide an image synthesizing method and the apparatus therefor with which an object body can be observed while freely moving a light source position.